CN115732578A - Double-sided equal-cathode annular gap spiral silicon drift detector and design method thereof - Google Patents
Double-sided equal-cathode annular gap spiral silicon drift detector and design method thereof Download PDFInfo
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Abstract
The invention discloses a spiral silicon drift detector, which comprises a base body, wherein the front surface and the back surface of the base body are in the same regular hexagon and are aligned in parallel, the center of the front surface of the base body is an anode for collecting electrons, the outer ring of the anode is provided with a front surface spiral ring cathode which extends outwards spirally along a hexagonal track, the center of the back surface of the base body is provided with a back surface cathode ring, the edge of the cathode is provided with a back surface spiral ring cathode which extends outwards spirally along the hexagonal track, the front surface spiral ring cathode and the back surface spiral ring cathode are both positioned in a boundary ring at the edge part of the base body, and the spaces of the front surface spiral ring cathode and the back surface spiral ring cathode are corresponding. The invention also discloses a design method of the detector. The detector of the invention adopts a hexagonal base body and a double-sided spiral ring cathode, and bias voltage is applied on the hexagonal base body and can form a uniform voltage gradient, thereby ensuring that electrons of an electron drift channel in a silicon substrate are uniformly distributed and being beneficial to improving the detection performance.
Description
Technical Field
The invention relates to the technical field of semiconductor detectors, in particular to a double-sided equal-cathode ring gap spiral silicon drift detector and a design method thereof.
Background
The silicon drift detector is a semiconductor detector for detecting energy beams, is based on the particularity of the structure of the silicon material and the superior electrical characteristics, and has important application in the aspects of modern medicine, nuclear technology, high-resolution X-ray spectrum and the like along with the improvement of scientific technology and the continuous and perfect process.
Under the working state of reverse bias voltage, the silicon drift detector generates electron-hole pairs around the drift path, can convert the energy of the energy beam into an electric signal which can be output, and after the electric signal is subjected to signal analysis, the signal reflects the characteristics of the energy beam, thereby achieving the purpose of detection.
The spiral silicon drift detector is a main product of an SDD family, the working principle of the spiral silicon drift detector can be regarded as a PN junction, and due to the geometrical structural characteristics of the spiral silicon drift detector, ion implantation is used as a rectifying junction and a voltage divider, and a potential gradient (or a drift field) is required to be created for the drift of carriers generated by incident particles to a collecting anode.
Compared with other types of detectors (such as a three-dimensional detector, a concentric silicon drift detector and the like), the spiral silicon drift detector is simpler in process manufacturing, a planar process is applied, heavy doping is only carried out on the surface of a silicon substrate, doping is carried out in an ion implantation mode, a P pole and an N pole are formed through different doping concentrations, and the simple process manufacturing enables the process cost to be relatively low. When the silicon substrate is in work, proper reverse bias voltage is applied to the central anode to enable the whole silicon substrate to reach a depletion state, so that an electron distribution similar to an electron channel is formed in the silicon substrate, the channel is very obvious, and the silicon substrate has good performance in work sensitivity, frequency response speed, collection efficiency and position resolution.
Chinese patent publication No. CN 109671797B, "drift detector and manufacturing method thereof", the drift detector includes: the tunneling oxide layer is formed on the first conductive semiconductor substrate; the second conductive semiconductor layer and the first conductive semiconductor substrate are opposite in conductive type, the third conductive semiconductor layer and the first conductive semiconductor substrate are the same in conductive type, the second conductive semiconductor layer, the tunneling oxide layer below the second conductive semiconductor layer and the first conductive semiconductor substrate jointly form a PN junction, and the PN junction is formed by the following steps: the drift electrode, the first protective ring, the incidence window and the second protective ring; the third conductive semiconductor layer, the tunneling oxide layer positioned below the third conductive semiconductor layer and the first conductive semiconductor substrate jointly form a high-low junction, and the high-low junction forms: an anode, a first ground electrode, and a second ground electrode. The drift detector realizes large area, low noise and high energy resolution.
The concentric ring drift detector has larger inter-ring gaps, so that the area of silicon oxide on the inter-ring gaps is larger, and the surface leakage current caused by the electronic state of the silicon oxide and the silicon interface is increased; meanwhile, the concentric ring structure cannot automatically divide the voltage, different bias voltages need to be applied to each concentric ring in order to ensure that the rings are changed according to a certain voltage gradient during pressurization, and the bias voltage application process is complex.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a double-sided equal-cathode annular gap spiral silicon drift detector and a design method thereof, which are used for solving the problem that the partial pressure cannot be automatically divided in the bias voltage application process in the prior art.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a double-sided equal-cathode ring gap spiral silicon drift detector comprises a base body, wherein the front surface and the back surface of the base body are in the same regular hexagon shape and are aligned in parallel, the positive center of the base body is an anode for collecting electrons, a positive spiral ring cathode is wound outside the anode and extends along a hexagonal track, a negative cathode ring is arranged in the center of the back surface of the base body, a negative spiral ring cathode is wound outside the spiral and extends along the hexagonal track and extends along the edge of the negative cathode ring, the positive spiral ring cathode and the negative spiral ring cathode are both positioned in a boundary ring at the edge part of the base body, and the space corresponding relation of the positive spiral ring cathode and the negative spiral ring cathode enables an electron drift channel formed in the base body after the detector automatically divides the voltage under bias voltage to tend to be a plane.
Furthermore, the positive spiral ring cathode and the negative spiral ring cathode are mirror images of each other, the gaps between the spiral ring rings of adjacent ring stages are equal, and the width of the spiral ring cathode is gradually increased along the spiral track extending outwards.
The cathode structure further comprises a hexagonal cathode ring positioned between the anode and the positive spiral ring cathode, wherein the anode is in a regular hexagon shape, the negative cathode ring is in a regular hexagon shape, and the hexagonal cathode ring and the negative cathode ring are similar to the anode in a concentric mode.
Further, the anode, the hexagonal cathode ring and the spiral ring cathode are aligned towards corresponding angles in six directions, and the starting point of the spiral ring cathode is located at the position of the angle.
Furthermore, the surfaces of the anode, the hexagonal cathode ring, the reverse cathode ring, the boundary ring, the starting part of the positive spiral ring cathode and the starting part of the reverse spiral ring cathode are all covered with aluminum electrode contact layers, and the areas between the positive spiral ring cathode and the reverse spiral ring cathode of the substrate are all covered with S i O 2 And (3) a membrane.
Furthermore, the size of the matrix is 3000 μm × 3000 μm × 300 μm, the radius of the circumscribed circle of the anode is 60 μm, the radius of the inscribed circle of the hexagonal cathode ring is 70 μm and the ring width is 20 μm, the distance from the starting point of the front spiral ring cathode to the center of the front surface of the matrix is 100 μm, the number of ring turns of the front spiral ring cathode is 21 turns, the inter-ring gap is 10 μm, the radius of the circumscribed circle of the back cathode ring is 80 μm and the ring width is 19 μm, and the inner diameter of the boundary ring is 2940 μm and the ring width is 60 μm;
the doping concentration of the matrix is 4 multiplied by 10 11 /cm 3 The doping depth is 1 mu m, and the doping concentration of the anode is 1 x 10 19 /cm 3 N-type heavy doping with doping depth of 1 μm, wherein the doping concentration of the hexagonal cathode ring, the reverse cathode ring and the boundary ring is 1 × 10 19 /cm 3 And the doping depth is 1 mu m.
The invention also discloses a design method of the double-sided equal-cathode annular gap spiral silicon drift detector, which comprises the following steps:
s1, setting an applied surface electric field E (r), a gap g between the E (r) and a ring, a pitch p (r) of a spiral ring cathode, a width omega (r) of the spiral ring cathode and a resistivity rho s The corresponding relation between the current I and the constant coefficient alpha of each stage of the ring length of the spiral ring cathode is as follows:
then there is a calculation of the pitch p (r):
and according to the relationship between the width omega (r) of the spiral ring cathode and the screw pitch p (r) and the inter-ring gap g of the spiral ring cathode, obtaining the following formula:
s2, iteratively solving sigma in the calculation formula (3) through a surface potential phi (R) formula, wherein:
in the above formula (5), phi I ＝4ρ s αI；x＝σ 2 r 2ε -1；x 1 ＝σ 2 r 1 2ε -1；n＝0,1,2,3Λ；
r is the radius which continuously extends outwards along with the angle of the spiral ring, r 1 Is the radius of the innermost ring, and R is the radius of the outermost ring;
and S3, calculating according to the formula in the S2:
s4, according to the formula in S3, calculating the radius r continuously extending outwards along the angle of the spiral ring:
in formula (7)
The radian is continuously increased in the positive and negative spiral rotation;
s5, substituting the formula (3) according to the calculation results sigma and r in the S3 and the S4 to obtain the width omega (r) of the spiral ring cathode;
s6, calculating depletion voltage
Wherein N is eff Is silicon substrate lightly doped with N-typeEffective doping concentration, q is the charge per electron q =1.6 × 10 -19 C，ε 0 Is a vacuum dielectric constant ε 0 ＝8.854×10 -12 F/m，ε Si Is the relative dielectric constant ε of silicon Si =11.9,d is the thickness d of the substrate.
Further, the surface electric field E (r) =120V, the inter-annular gap g =10 μm, the thickness d =300 μm of the base body, and the radius r 1 =100 μm, radius R of outermost ring =2500 μm, resistivity ρ s =2000 (ψ · cm), dielectric constant ∈ =1, and current I =0.05mA.
The spiral structure adopted by the scheme has the function of automatic voltage division, and after different bias voltages are added on the innermost side and the outermost side of the spiral ring, an even voltage gradient can be automatically formed, so that automatic voltage division is achieved. The center of the front surface of the detector is made into an anode for collecting electrons, other electrodes on the front surface and the back surface are made into cathodes, so that an optimal symmetrical effect is achieved, a surface electric field and a ring gap of the equal cathode are given, when particles are driven into the detector from an incident surface, an electric field parallel to the surface is formed between the upper surface and the lower surface, an optimal electron drift channel is obtained, and the detection performance of the detector can be improved.
Drawings
FIG. 1 is a top plan view and partially enlarged view of a detector in accordance with an embodiment of the present invention.
FIG. 2 is a top view of a detector in an embodiment of the invention, with a partial enlarged view.
FIG. 3 is an X-axis cross-sectional view and a partial enlarged view of a detector in an embodiment of the invention.
FIG. 4 is a diagram illustrating the simulation of the electric field of the detector under the voltages of 84V at the outermost ring of the positive spiral ring cathode and 75V at the outermost ring of the negative spiral ring cathode in one embodiment of the present invention.
FIG. 5 is a potential simulation diagram of the detector under the voltages of 84V at the outermost ring of the positive spiral ring cathode and 75V at the outermost ring of the negative spiral ring cathode in one embodiment of the invention.
FIG. 6 is a simulation diagram of electron concentration of the detector under the voltages of 84V at the outermost ring of the positive spiral ring cathode and 75V at the outermost ring of the negative spiral ring cathode in one embodiment of the invention.
Figure 7 is a graph of the electric field comparison of one-dimensional cross-section for a detector according to one embodiment of the invention and a comparative example at z =150 μm.
Fig. 8 is a graph of electron concentration in one-dimensional cross-section for a detector according to an embodiment of the present invention compared to a comparative example at Y =0 μm.
In the figure: 1. an anode; 2. a hexagonal cathode ring; 3. a front spiral ring cathode; 4. s i O 2 A film; 5. starting point of the positive spiral ring cathode; 6. a boundary ring; 7. s i O 2 A film; 8. a reverse cathode ring; 9. starting point of negative spiral ring cathode; 10. a reverse spiral ring cathode; 11. a boundary ring; 12. an aluminum electrode contact layer covering the anode; 13. an aluminum electrode contact layer covered on the hexagonal cathode ring; 14. an aluminum electrode contact layer covered on the negative spiral ring cathode.
Detailed Description
The technical solutions in the embodiments disclosed in the present application will be described clearly and completely with reference to the drawings in the embodiments disclosed in the present application, and it is obvious that the embodiments described are only some embodiments of the present disclosure, not all embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments disclosed in the present application without making any creative effort, shall fall within the scope of the protection of the present disclosure.
The relative arrangement of the components and steps, the numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present disclosure unless specifically stated otherwise.
Meanwhile, it should be understood that the sizes of the respective portions shown in the drawings are not drawn in an actual proportional relationship for the convenience of description.
Techniques, methods, and apparatus known to one of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate.
In all examples shown and discussed herein, any particular value should be construed as exemplary only and not as limiting. Thus, other examples of the exemplary embodiments may have different values.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, further discussion thereof is not required in subsequent figures.
The present invention will be described in further detail with reference to the following embodiments and the accompanying drawings.
A double-sided equal-cathode ring gap spiral silicon drift detector is shown in figures 1-3 and comprises a base body, wherein the front surface and the back surface of the base body are in the same regular hexagon shape and are aligned in parallel, an anode 1 for collecting electrons is arranged in the center of the front surface of the base body, a front spiral ring cathode 3 which is spirally outward and extends along a hexagonal track is arranged outside the anode 1, a back cathode ring 8 is arranged in the center of the back surface of the base body, a back spiral ring cathode 10 which is spirally outward and extends along the hexagonal track is arranged around the edge of the back cathode ring 8, the front spiral ring cathode 3 and the back spiral ring cathode 10 are both positioned in boundary rings 6 and 11 at the edge part of the base body, and the electron drift channels formed in the base body after the detector automatically divides the voltage under bias voltage tend to be a plane due to the spatial correspondence of the front spiral ring cathode 3 and the back spiral ring cathode 10.
The spiral structure that the negative pole of this scheme adopted has the function of automatic partial pressure, after adding different bias voltages at spiral ring the innermost and outermost, will form an even voltage gradient automatically to reach automatic partial pressure, positive pole 1 that the positive center of detector was made and is collected the electron, and positive and negative two sides other electrodes are all made the negative pole, thereby reach an optimum symmetrical effect, can obtain an optimum electron drift passageway. The surface electric field given by the detector can be effectively adjusted according to actual conditions to realize the optimal carrier drift electric field, so that the function optimization of the detector is realized. According to the prior art, the spiral ring can achieve a micro-nano level double-sided process, the process technology is mature, and the position resolution is high. The boundary rings 6, 11 are guard rings and protect the outermost ring electrodes from breakdown due to high voltage. For the sake of simplicity, the spiral ring or spiral ring cathode refers to the front spiral ring cathode 3 and the back spiral ring cathode 10.
The positive spiral ring cathode 3 and the negative spiral ring cathode 10 are mirror images of each other, that is, the radial plane of the substrate is taken as a symmetrical plane, the positive spiral ring cathode 3 and the negative spiral ring cathode 10 are symmetrical, and the projections of the positive spiral ring cathode 3 and the negative spiral ring cathode 10 in the X-axis direction are completely overlapped with the gaps between the spiral ring rings. Gaps between the spiral rings of adjacent ring stages are equal, and the width of the spiral ring cathode is gradually increased along the spiral track extending outwards.
The cathode ring clearance such as this scheme is for having along with the design of cathode ring radius increase and the clearance of grow gradually a great deal of advantage. First, the area of silicon oxide on the cathode ring gap can be controlled and minimized, thereby minimizing surface leakage current due to the electronic state at the silicon oxide and silicon interface. And then the cathode gap ring can be effectively and controllably adjusted to achieve better surface electric field distribution. In the design, the surface electric field can be effectively adjusted according to the actual situation to realize the optimal carrier drift electric field, thereby realizing the optimization of the function of the detector.
Compared with a quadrilateral silicon drift detector, the scheme adopts the hexagonal base body and the cathode in the shape of the spiral ring, the distribution of the cathode is closer to a circle, the distance between the anode 1 and the cathode is more uniform and the symmetry is better, and a bias voltage is applied to the cathode to form a uniform voltage gradient, so that the uniform distribution of electrons of an electron drift channel in a silicon substrate is ensured, a better electron drift channel is obtained, and the improvement of the detection performance is facilitated. Simultaneously, compare in circular shape base member, this scheme adopts the hexagon, and it is when as array unit, can closely arrange, and no space can realize surveying no dead zone between the unit.
As a preferred embodiment, the cathode structure further comprises a hexagonal cathode ring 2 positioned between the anode 1 and the front spiral ring cathode 3, wherein the anode 1 is a regular hexagon, the back cathode ring 8 is a regular hexagon ring, and the hexagonal cathode ring 2 and the back cathode ring 8 are similar to the anode 1 in a concentric mode.
Obviously, because of the symmetry of the spiral parts on the front and back sides, the anode 1, the hexagonal cathode ring 2 and the spiral ring cathode are aligned to the corresponding corners of six directions for achieving the optimal cathode arrangement density and uniformity, and the starting point of the spiral ring cathode is located at the corner position.
The surfaces of the anode 1, the hexagonal cathode ring 2, the reverse cathode ring 8, the boundary rings 6 and 11, the starting point 5 of the positive spiral ring cathode 3 and the starting point 9 of the reverse spiral ring cathode 10 are all covered with aluminum electrode contact layers, and aluminum films with the thickness of 1 mu m are covered at the positions where the electrodes are contacted for the front electrode contact of the detector. Namely an aluminum electrode contact layer 12 covered on the anode, an aluminum electrode contact layer 13 covered on the hexagonal cathode ring, and an aluminum electrode contact layer 14 covered on the reverse spiral ring cathode. The cathode ring-to-ring area of the spiral rings on the front and back surfaces of the substrate are covered with SiO2 films 4 and 7, namely, the silicon dioxide with the depth of 0.5 mu m is covered on the places without electrode contact on the two surfaces to prevent the silicon substrate from being oxidized.
V out = -84V applied to outermost ring of front spiral-ring cathode 3, V E1 = 6v is applied at the starting point of the front spiral-ring cathode 3,
applied to the outermost rings of the reverse spiral ring cathode 10,
applied to the starting position of the reverse spiral ring cathode 10.
As an example, a substrate having dimensions of 3000. Mu. M.times.3000. Mu. M.times.300. Mu.m is used, and FIG. 1 shows the probeThe front view of the device, the center is a collecting anode 1, the radius of the anode 1 is 60 μm, the doping concentration of the anode 1 is 1 × 10 19 /cm 3 The N type heavy doping is 1 μm, the cathode composed of a cathode ring and a spiral ring electrode is arranged outside the anode 1, the radius of the cathode ring is 70 μm, the ring width is 20 μm, the radius of the innermost starting position of the spiral ring is 100 μm, the radius of the outermost tail end of the spiral ring at the front side is the same as that of the front side protection ring, and the front side protection ring form a part, the radius of the front side protection ring is 2940 μm, the ring width is 60 μm, the cathode has the doping concentration of 1 x 10 19 /cm 3 The doping depth is 1 mu m; the substrate is N-type lightly doped with a doping concentration of 4 × 10 11 /cm 3 (ii) a FIG. 2 is a reverse view of the detector, the reverse side has no anode 1, the cathode is composed of a cathode ring and a spiral ring, the radius of the cathode ring is 80 μm, the ring width is 19 μm, the radius of the innermost starting position of the spiral ring is 100 μm, the radius of the outermost end position of the spiral ring is the same as that of the reverse side protection ring, and the reverse side protection ring forms a part with the reverse side protection ring, the radius of the reverse side protection ring is 2940 μm, the ring width is 60 μm, the doping concentration is 1 × 10 19 /cm 3 The doping depth is 1 mu m; the number of the spiral ring turns on the front face and the back face is 21.
The helical ring gap is the distance between the outer boundary of a certain ring of the helical ring-shaped cathode and the inner boundary of an adjacent ring outside, and then the pitch p (r) of the helical ring cathode is the sum of the width omega (r) of the current helical ring cathode and the helical ring gap g. The cathode structure can effectively and controllably adjust the width omega (r) of the spiral ring and the pitch p (r) occupied by the ring level, and can achieve better surface electric field distribution and straighten the drift channel. In the design, the surface electric field can be effectively adjusted according to the actual situation to realize the optimal carrier drift electric field, thereby realizing the optimization of the function of the detector. When particles are driven into the detector from the incident surface, an electric field distribution parallel to the surface is formed between the front surface and the back surface, so that an optimal electron drift channel can be obtained.
When designing the detector, the optimal surface potential distribution of electrons is calculated by theory, the surface electric field and the gap tolerance between rings are given, and the specific structure size of the detector is designedAnd an internal configuration. In general, to avoid possible singularities of the electric field at R = R, the values of Vout and Vb will have an upper limit, and for the double-sided symmetric helical SDD herein, vout is generally less than four times the depletion voltage Vfd, because Vout must be large enough to ensure a suitable drift electric field, especially for the case where the radius R is too large. In this context, the detector radius R =3000 μm, the electrode contact is reverse biased, V out ＝-84v，V E1 ＝-6v，
The design method comprises the following steps:
s1, setting an applied surface electric field E (r), a gap g between the E (r) and a ring, a pitch p (r) of a spiral ring cathode, a width omega (r) of the spiral ring cathode and a resistivity rho s The corresponding relation between the current I and the constant coefficient alpha of each stage of the spiral ring cathode is as follows:
then the calculation of the pitch p (r):
and according to the relationship between the width omega (r) of the spiral ring cathode and the pitch p (r) and the gap g between the rings of the spiral ring cathode, obtaining:
a is the coefficient between the radius and the length of the single turn helix, the number of lengths of the helical loops per turn varies depending on the helical geometry, the invention uses a regular hexagonal type structure, the length of the helical loops per turn = ar =6r.
S2, iteratively solving sigma in the calculation formula (3) through a surface potential phi (R) formula, wherein:
in the above formula (5), phi I ＝4ρ s αI；x＝σ 2 r 2ε -1；x 1 ＝σ 2 r 1 2ε -1；n＝0,1,2,3Λ；
r is the radius which continuously extends outwards along with the angle of the spiral ring, r 1 Is the radius of the innermost ring and R is the radius of the outermost ring.
By effectively and controllably adjusting the cathode gap g, better surface electric field distribution is obtained, meanwhile, the area of silicon oxide between gaps is optimally reduced, and the surface leakage current caused by the electronic state of the silicon oxide and the silicon interface is reduced to the maximum extent.
And S3, calculating according to the formula in the S2:
s4, according to the formula in S3, calculating the radius r continuously extending outwards along the angle of the spiral ring:
in formula (7)
The radian of the continuous increment in the positive and negative spiral rotation can be designed and calculated according to relevant parameters
And (4) obtaining.
S5, substituting the formula (3) according to the calculation results sigma and r in the S3 and the S4 to obtain the width omega (r) of the spiral ring cathode;
s6, calculating depletion voltage
Wherein N is eff For the silicon matrix N-type light doping effective doping concentration, q is the charge quantity of each electron q =1.6 × 10 -19 C，ε 0 Is a vacuum dielectric constant ε 0 ＝8.854×10 -12 F/m，ε Si Is the relative dielectric constant ε of silicon Si =11.9,d is the thickness d of the substrate.
The given parameters of the formula of the steps can be changed according to the actual situation. As described, the surface electric field E (r) =120V, the inter-annular gap g =10 μm, the thickness d =300 μm, and the radius r of the substrate 1 =100 μm, radius R of outermost ring =2500 μm, resistivity ρ s =2000 (ψ · cm), dielectric constant ∈ =1, and current I =0.05mA.
The surface electric field can be effectively adjusted according to the actual situation in the design so as to realize the optimal carrier drift electric field, thereby realizing the optimization of the function of the detector. By combining the data of the above embodiments, a detector of a specific product can be designed, and a simulation test is performed on the detector, and when a bias voltage is applied, the voltage of the innermost ring stage is 65V under the voltages of 84V at the outermost ring of the front spiral ring cathode 3 and 75V at the outermost ring of the back spiral ring cathode 10, and the test results are shown in fig. 4 to 6, it can be seen that the electric field distribution is uniform, the potential distribution is in a gradient such as a smooth trend, and the electron concentration in the electron drift channel is uniform. The obtained electron drift channel approaches to a plane and approaches to the theoretical optimal electron drift channel form.
We can use a single-sided helical silicon drift detector for comparison of electron drift channels, when both form the best electron channel, as shown in figure 7 for the electric field contrast plot (z =150 μm) of one-dimensional cross-section for both double-sided and single-sided structures. As can be seen from fig. 7, the lateral drift electric field of the double-sided structure is larger and more uniform, and the low electric field area is smaller, so that the drift trajectory is more obvious, and the electron collection time is faster, compared with the previous single-sided structure.
Fig. 8 is an electron concentration comparison graph (when Y =0 μm) of one-dimensional cross-section of the double-sided and single-sided structures, and it can be seen from the comparison graph that the curve of the double-sided structure is more constant than that of the single-sided structure, and the incident particle first moves into the drift channel under the driving of the high electric field of the double-sided structure, and then drifts to the central anode collector 1 under the driving of a nearly constant electric field in the drift channel, so that the response speed is improved.
Compared with the automatic voltage division function of the concentric ring detector, the spiral silicon drift detector has the advantages that different bias voltages need to be applied to each concentric ring of the concentric ring detector when pressurization is needed to ensure that the rings are changed according to a certain voltage gradient, and obviously, the detector is simpler to operate when in use. The manufacturing process technology of the three-dimensional detector has certain difficulties, the effect of an etching area is poor during etching, the doping positions among different levels are different, the process is very complicated, and a silicon substrate has an area with a small electric field or a zero electric field area; according to the scheme, the wafer defects can be eliminated by using a zone melting method in the gettering oxidation process link, a double-sided photoetching alignment mark manufacturing process is used in the photoetching mark manufacturing link, a set of mark point mask plates are added before photoetching to align the position of a detector, double-sided process single-sided photoetching is used in the ion implantation process link, the front side and the back side are completed separately during manufacturing, and the back side glue homogenizing is dried and protected during front side process.
The technical solutions provided by the embodiments of the present invention are described in detail above, and the principles and embodiments of the present invention are explained herein by using specific examples, and the descriptions of the embodiments are only used to help understanding the principles of the embodiments of the present invention; meanwhile, for a person skilled in the art, according to the embodiments of the present invention, there may be variations in the specific implementation manners and application ranges, and in summary, the content of the present description should not be construed as a limitation to the present invention.
Claims (8)
1. The utility model provides a two-sided isocathode ring gap screw-tupe silicon drift detector which characterized in that: the detector comprises a base body with the front and back surfaces being in the same regular hexagon and aligned in parallel, wherein the center of the front surface of the base body is an anode for collecting electrons, the outer ring of the anode is wound with a front spiral ring cathode which extends outwards spirally along a hexagonal track, the center of the back surface of the base body is provided with a back surface cathode ring, a back surface spiral ring cathode which extends outwards spirally along a hexagonal track is wound along the edge of the back surface cathode ring, the front surface spiral ring cathode and the back surface spiral ring cathode are both positioned in a boundary ring at the edge part of the base body, and the space corresponding relation of the front surface spiral ring cathode and the back surface spiral ring cathode enables an electron drift channel formed in the base body after the detector automatically divides the voltage under bias voltage to tend to be a plane.
2. The double-sided equi-cathode ring gap spiral type silicon drift detector of claim 1, wherein: the positive spiral ring cathode and the negative spiral ring cathode are mirror images of each other, gaps between the spiral rings of adjacent ring stages are equal, and the width of the spiral ring cathode is gradually increased along a spiral track extending outwards.
3. The double-sided equi-cathode ring gap spiral silicon drift detector of claim 2, wherein: the cathode structure also comprises a hexagonal cathode ring positioned between the anode and the positive spiral ring cathode, wherein the anode is in a regular hexagon shape, the negative cathode ring is in a regular hexagon shape, and the hexagonal cathode ring and the negative cathode ring are concentric and similar to the anode.
4. The double-sided equi-cathode ring gap spiral type silicon drift detector of claim 3, wherein: the anode, the hexagonal cathode ring and the spiral ring cathode are aligned towards corresponding angles in six directions, and the starting point of the spiral ring cathode is located at the position of the angle.
5. A double-sided equi-cathode ring gap spiral silicon drift detector as claimed in any one of claims 1 to 4, wherein: the surfaces of the anode, the hexagonal cathode ring, the reverse cathode ring, the boundary ring, the starting part of the positive spiral ring cathode and the starting part of the reverse spiral ring cathode are all covered with aluminum electrode contact layers, and the areas between the positive spiral ring cathode and the reverse spiral ring cathode of the matrix are all covered with S i O 2 And (3) a film.
6. The double-sided equi-cathode ring gap spiral silicon drift detector of claim 5, wherein: the size of the matrix is 3000 micrometers multiplied by 300 micrometers, the radius of the circumscribed circle of the anode is 60 micrometers, the radius of the inscribed circle of the hexagonal cathode ring is 70 micrometers, the ring width is 20 micrometers, the distance from the starting point of the positive spiral ring cathode to the center of the front surface of the matrix is 100 micrometers, the ring-level turn number of the positive spiral ring cathode is 21 turns, the inter-ring gap is 10 micrometers, the radius of the circumscribed circle of the negative cathode ring is 80 micrometers, the ring width is 19 micrometers, and the inner diameter of the boundary ring is 2940 micrometers, and the ring width is 60 micrometers;
the doping concentration of the matrix is 4 multiplied by 10 11 /cm 3 The doping depth is 1 mu m, and the doping concentration of the anode is 1 x 10 19 /cm 3 N-type heavy doping with doping depth of 1 μm, wherein the doping concentration of the hexagonal cathode ring, the reverse cathode ring and the boundary ring is 1 × 10 19 /cm 3 And the doping depth is 1 mu m.
7. The design method of a double-sided plasma cathode circular gap spiral type silicon drift detector as claimed in any one of claims 1 to 6, comprising the steps of:
s1, setting an applied surface electric field E (r), a gap g between the E (r) and a ring, a pitch p (r) of a spiral ring cathode, a width omega (r) of the spiral ring cathode and a resistivity rho s The corresponding relation between the current I and the constant coefficient alpha of each stage of the spiral ring cathode is as follows:
then there is a calculation of the pitch p (r):
and according to the relationship between the width omega (r) of the spiral ring cathode and the screw pitch p (r) and the inter-ring gap g of the spiral ring cathode, obtaining the following formula:
s2, iteratively solving sigma in the calculation formula (3) through a surface potential phi (R) formula, wherein:
in the above formula (5), phi I ＝4ρ s αI；x＝σ 2 r 2ε -1；x 1 ＝σ 2 r 1 2ε -1；n＝0,1,2,3Λ；
r is the radius which continuously extends outwards along with the angle of the spiral ring, r 1 Is the radius of the innermost ring, and R is the radius of the outermost ring;
and S3, calculating according to the formula in the S2:
s4, according to the formula in S3, calculating the radius r continuously extending outwards along the angle of the spiral ring:
in formula (7)
The radian is continuously increased in the spiral rotation of the front surface and the back surface;
s5, substituting the formula (3) according to the calculation results sigma and r in the S3 and the S4 to obtain the width omega (r) of the spiral ring cathode;
s6, calculating depletion voltage
Wherein N is eff For silicon matrix N-type lightly doped effective doping concentration, q is charge amount per electron q =1.6 × 10 -19 C，ε 0 Is a vacuum dielectric constant ε 0 ＝8.854×10 -12 F/m，ε Si Is the relative dielectric constant ε of silicon Si =11.9,d is the thickness d of the substrate.
8. The design method of the double-sided plasma cathode circular gap spiral type silicon drift detector of claim 7, characterized in that: the surface electric field E (r) =120V, the inter-annular gap g =10 μm, the thickness d =300 μm of the substrate, and the radius r 1 =100 μm, radius R of outermost ring =2500 μm, resistivity ρ s =2000 (ψ · cm), dielectric constant ∈ =1, and current I =0.05mA.
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